Theoretical methodology for prediction of tropospheric oxidation of dimethyl phosphonate and dimethyl methylphosphonate.

Rate constants for the reactions of OH radicals with dimethyl phosphonate [DMHP, (CH(3)O)(2)P(O)H] and dimethyl methylphosphonate [DMMP, (CH(3)O)(2)P(O)CH(3)] have been calculated by ab initio structural methods and semiclassical dynamics modeling and compared with experimental measurements over the temperature range 250-350 K. The structure and energetics of reactants and transition structures are determined for all hydrogen atom abstraction pathways that initiate the atmospheric oxidation mechanism. Structures are obtained at the CCSD/6-31++G** level of chemical theory, and the height of the activation barrier is determined by a variant of the G2MP2 method.

Calcium and calcitriol prophylaxis attenuates posttransplant bone loss.

We performed a prospective, randomized, double-blind study to determine whether calcium and calcitriol prevents posttransplant bone loss. Thirty-eight nondiabetic and 26 diabetic patients without prior steroid exposure undergoing their first kidney or kidney-pancreas transplant were randomized to calcium, calcium plus calcitriol, or placebo. Lumbar spine (LS), femoral neck (FN), and distal radius (DR) bone mineral density scans (BMDs) were obtained at baseline, 6, and 12 months.